Experiments will continue on the role of the Pi binding site in the mechanism of action of the mitochondrial ATPase. Adenine nucleotides will be used to probe the location of the Pi binding site as well as to study the nature of the interaction of Pi with ADP on the enzyme and to monitor rapid conformational changes and relaxation effects in the protein. Conformational changes and relaxation effects in the oligomycin-sensitive ATPase also will be investigated using the rate of Pi binding and displacement as a measure of alterations in the structure of this form of the enzyme.